I only really understand your first question
If you have eye strain your optometrist should consider doing cyclopentolate refraction or using prism. Your case history, cause of strain and has a recent change in your prescription prompted it all matter. Poor sleep and stress can cause it too.
Prism corrects binocular vision. Remember you have 2 eyes but only see 1 image. There’s an entire network of muscles and nerves that work together to ensure you see one image.
I have prism in my own lenses as I get some eyestrain sitting in my office all day. It’s not a big deal to get either and can make a major difference to your eyes
Prism has other uses too btw